The invention relates to a lighting device for a motor vehicle.
The prior art has disclosed lighting devices for motor vehicles comprising a scanner, by means of which a predetermined light distribution in the far field of the vehicle is generated by means of the deflection of a light beam via a reflecting scanning mirror.
In the case of lighting devices comprising a scanner, it is found to be disadvantageous that the deflection frequency of the scanning mirror has to be very high in order to generate structures in the light distribution with a high resolution or with strong gradients. This leads to bothersome scanning effects, such as the stroboscopic effect, particularly at high vehicle speeds. In order to generate light/dark boundaries, scanning lighting devices require a very high optical resolution so as to be able to produce the necessary gradients in the light distribution. Furthermore, the practice of introducing physical stops into the beam path of the light beam for generating light/dark boundaries is known. However, these are disadvantageous in that, in general, they lead to shadowing effects in the generated light distribution.
It is an object of the invention to develop a lighting device for a motor vehicle, by means of which a light distribution with a high quality can be produced.
This object is achieved by the lighting device in accordance with the independent claims. Developments of the invention are defined in the dependent claims.
The lighting device according to the invention is provided for a motor vehicle such as e.g. a passenger car or a truck. It comprises a light source made of a number of semiconductor diodes and a scanning apparatus, onto which light from the light source is incident and which, when the lighting device is in operation, produces a time-varying deflection of the incident light from the light source and, thereby, a predetermined light distribution at a distance from the lighting device. Here, the predetermined light distribution is generated in the far field of the lighting device in particular. Here, the far field should be understood to mean the light distribution at a distance from the lighting device, which is substantially greater than the dimensions of the lighting device and, in particular, lies in the region of 25 m in front of the lighting device.
The lighting device according to the invention is distinguished by virtue of the fact that the scanning apparatus installed therein comprises at least two separately actuatable scanners, onto which in each case a separate light beam produced from the light of the light source is incident, the deflection of which light beam is varied in time by the respective scanner. Here, a light beam should be understood to mean a beam of light rays within a restricted angle or space, wherein the light rays in the bundle may extend substantially parallel to one another or else may diverge or converge. Therefore, the scanning apparatus comprises at least two separate scanners with assigned deflection elements which, in particular, are embodied as reflecting scanning mirrors. By the separate actuation of the scanners, the deflection elements can independently of one another cause a time variation in the deflection of the corresponding light beam. By using more than one scanner, the deflection frequency of the individual scanners can be reduced in the case of an unchanged resolution or an unchanged gradient in the light distribution, as a result of which bothersome scanning effects, which occur at high vehicle velocities in particular, are avoided.
In a particularly preferred embodiment of the lighting device according to the invention, one or more of the scanners and, in particular, all of the scanners of the scanning apparatus in each case comprise a two-dimensional scanning unit, by means of which the corresponding light beam can be deflected in two directions and, in particular, in a horizontal and in a vertical direction. Here, the horizontal and vertical directions relate to the lighting device in the assembled state in the vehicle, i.e. the vertical direction extends perpendicularly upward from the roadway and the horizontal direction extends parallel to the roadway. Here, the two-dimensional scanning unit can be embodied as a 2D scanner with an individual deflection element or scanning mirror swivelable in two directions. Optionally, the two-dimensional scanning unit can also be formed by two deflection elements or scanning mirrors which are actuated together. In a particularly preferred embodiment, the scanners of the lighting device according to the invention are, at least in part, vector scanning units, in which the scanning speed and scanning direction can be varied.
In a further embodiment, the lighting device according to the invention comprises at least one entrance optical means for the light from the light source, wherein, when the lighting device is in operation, the separate light beams are produced by way of the at least one entrance optical means. Preferably, a common entrance optical means is provided for producing all separate light beams. As a result of this, the setup of the lighting device becomes less complex. The entrance optical means may e.g. comprise a lens array, wherein a separate light beam is generated by each lens of the array. Here, a collimator lens for focusing the light originating from the light source is preferably disposed upstream of the lens array.
In a further, particularly preferred embodiment, the lighting device is configured in such a way that the separate light beams generate light spots with different sizes in the predetermined light distribution. This renders it possible, in a very flexible manner, to produce different light distributions with, in portions, different resolutions by means of the lighting device, and so the scanning lighting apparatus can assume the function of an adaptive optical element in the form of a lens with a variable refractive power.
In a further embodiment of the lighting device according to the invention, at least one exit optical means, by means of which the predetermined light distribution is generated as an image at a distance from the lighting device, is provided for the light beams deflected by the at least two scanners. Preferably, a common exit optical means is provided for all deflected light beams, as a result of which the setup of the lighting device is simplified.
In a further embodiment of the lighting device according to the invention, one or more of the scanners of the scanning apparatus in each case generate a separate region of the predetermined light distribution. However, alternatively or additionally, it is also possible for at least two scanners to generate overlapping regions of the predetermined light distribution.
In a further embodiment of the lighting device according to the invention, a stop, by means of which the light distribution can be delimited, is arranged in the beam path of the light beams after deflection by the scanning apparatus. In a preferred embodiment, a light/dark boundary is generated in the predetermined light distribution by the stop. The stop preferably extends substantially parallel to an optical axis predetermined by the beam path of the light beams.
In a particularly preferred embodiment, the stop brings about a subdivision of an image plane into two regions, wherein, in at least one mode of operation of the lighting device, a part of the scanning apparatus is provided exclusively for deflecting light beams in a region on one side of the stop and, in particular, below the stop and the other part of the scanners of the scanning apparatus is provided exclusively for deflecting light beams in a region on the other side of the stop and, in particular, above the stop. This renders it possible to avoid shadowing effects, which may occur when a scanning apparatus with a single scanner is used. For explanatory purposes, these shadowing effects will be returned to in more detail in the detailed description. In a preferred variant, the aforementioned image plane, which is subdivided into two regions, is an intermediate image plane which is imaged by an exit optical means into the predetermined light distribution at a distance from the lighting device.
Optionally, it is furthermore possible that, in addition or in place of the above-described stop, which is arranged in the beam path of the light beams after deflection by the scanning apparatus, provision made for one or more further stops at different positions in the beam path, e.g. in front of the scanning apparatus.
As an alternative or in addition to the above-described stop, provision is made in a further preferred embodiment for at least one scanner, exclusively for generating the light distribution at the light/dark boundary in at least one mode of operation of the lighting device (e.g. when generating a dipped beam characteristic). Here, this scanner can be operated with a higher deflection frequency than the other scanners or this scanner can generate a smaller light spot than the other scanners in the light distribution in order hereby to achieve high resolutions in the region of the light/dark boundary such that, optionally, it is possible to dispense with the use of physical stops for generating strong gradients in the light distribution. This is advantageous in that a gradient profile can be configured variably, i.e. independently of rigid physical stops, in a light distribution.
In a further embodiment of the lighting device according to the invention, the at least two scanners of the scanning apparatus are provided on a common assembly, wherein the common assembly includes, in particular, a common cooling unit and/or a common electronics unit for the scanners and/or a common mechanical adjustment apparatus for a support, on which the scanners are assembled. As a result, a simple setup of the scanning apparatus is achieved. Furthermore, due to the use of a plurality of scanners, a relatively large spread in the local temperature load on the cooling unit is ensured, which significantly reduces the installation space and the weight of the cooling elements employed in the cooling unit.
In a further variant, at least one scanner and, in particular, each one of the scanners of the scanning apparatus is embodied as a MEMS element, which allows a particularly compact and robust embodiment with high deflection speeds as a result of the micromechanical scanner setup thereof. In particular, these elements are suitable for an array-shaped arrangement on a common assembly and can also be employed for high-power applications in the automotive sector as a result of the distribution of the light fluxes to a plurality of units.
In a further variant, the number of semiconductor diodes comprises one or more and in particular exclusively laser diodes. As a result, it is possible to produce a light distribution with a very high local luminous intensity. The laser diodes preferably have a respective maximum power of at least 1 W and, in particular, of between 1.5 and 5 W. Preferably, the number of semiconductor diodes for generating the predetermined light distribution is operated with constant and, in particular, maximum power, as a result of which the lighting device is used particularly efficiently.
In a further embodiment of the invention, the light source is a monochromatic light source, wherein a conversion element is provided for converting the light from the light source into white light. Such conversion elements are known per se from the prior art. By way of example, in the case of blue/violet laser diodes with an emission wavelength of 450 nm/405 nm, it is possible to use a phosphor conversion element made of a nitride phosphor or an oxide nitride phosphor or a cerium-doped YAG phosphor for generating white light.
The conversion element, which is configured as a layer in particular, can be arranged at different positions depending on the embodiment of the invention. In one variant, the conversion element is arranged at a position at which the light beam has already passed through the scanning apparatus, e.g. in the aforementioned intermediate image plane. However, the conversion element can also be arranged at the light source or between the light source and the scanning apparatus. In the latter case, the conversion element is arranged at a position in the beam path of the light beam before the light beam is incident on the scanning apparatus.
Depending on the application, the lighting device according to the invention can assume various functionalities. In one embodiment, the lighting device comprises a headlamp. A headlamp is distinguished by virtue of the fact that it actively illuminates the surroundings of the vehicle. Optionally, the lighting device according to the invention may also comprise a signal light, which is distinguished by virtue of the fact that it only serves for providing signals to other traffic participants. Likewise, the lighting device according to the invention may be a combination of headlamp and signal light.
In a preferred variant, the lighting device is configured as a headlamp in such a way that, during operation, a dipped beam characteristic and/or a main beam characteristic can be generated as predetermined light distribution. A dipped beam characteristic is distinguished by a sharp light/dark boundary, which is preferably generated using the above-described stop. The scanner used in the region of the light/dark boundary preferably has a high or higher local resolution compared to other scanners of the scanning apparatus. This can be achieved by a light spot being generated by this scanner, said light spot having a smaller size than the light spots from the other scanners.
In addition to the lighting device according to the invention, the invention furthermore relates to a motor vehicle comprising one or more of the lighting devices according to the invention.
Exemplary embodiments of the invention are described in detail below on the basis of the attached figures.
In detail:
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.